While humans have contributed to the extinction of several turtle and tortoise species, DNA evidence shows Pelusios seychellensis is not one of them, a team from Germany and Austria write in the journal PloS One .

"The protection programs for turtles in the Seychelles will have to be revised so that truly endemic animal species are protected and the scarce funds available for species protection are put to good use," says study co-author Uwe Fritz from Dresden's Senckenberg Research Institute.

Genetic comparisons showed the species to be one and the same as a widespread West African turtle called Pelusios castaneus, of which a handful of individuals may have been brought to the archipelago by humans long ago, and mistaken for endemic.

Even more likely -- dried museum specimens of the now discredited P seychellensis were wrongly labelled as originating in the Seychelles, say the researchers.

Turtles and tortoises are the vertebrates at the greatest risk of extinction. Of about 320 species, those endemic to islands had been hardest hit, both by predators and human interference.

P seychellensis was originally described in 1906 as a species endemic to Mahé island.

Only three museum specimens from the late 19th century are known today, and live turtles were never found despite intensive searches of Mahé -- prompting the International Union for the Conservation of Nature to declare it extinct in 2003.

Scientists have puzzled over the turtle's physical similarity to P castaneus, but concluded the two must be distinct due to the vast geographical distance between them.

P castaneus is found from Senegal to Angola along the western coast of Africa -- separated from the Seychelles islands off the continent's east coast by the entire African landmass and a vast expanse of ocean.

It was therefore unlikely the human hand-sized turtle had made its way to the Seychelles by natural means to settle a colony abroad.

This left two possibilities -- either the museum specimen was mislabelled, or the turtle was transported by humans from West Africa to the Seychelles in the late 1800s, say the study authors.

"Owing to the considerable distance between West Africa and the Seychelles, the latter option seems less likely."

This would not be the first time that a museum labelling error gave the world a non-existing turtle species, they say.

A New Guinea species described in 1905 turned out to be a North American snapping turtle for which the data had been confounded.

And a Vietnamese species described in 1941 was later found to have been an escaped pet tortoise from Madagascar.

The same team of scientists had previously shown that another turtle species, P subniger, had been brought to the Seychelles from elsewhere -- leaving only one known mud turtle species that could possibly be endemic to the island group.